This invention relates to a method for purifying aqueous liquids. The invention is especially applicable to treating bodies of water which can be recirculated, such as swimming pools, holding ponds of refinery waste water disposal systems, reservoirs of municipal water supply systems, and the like.
At the present time, water in swimming pools is purified by adding chlorine. Muriatic acid also is frequently added to the water to maintain its pH near 7. The use of such chemicals in the swimming water causes several problems. Chlorine and muriatic acid are extremely poisonous, and even in their diluted state are irritating to the eyes and skin of persons in the water. Halogen-containing salts also cause salt build-up and evaporative losses of chlorine and muriatic acid are costly to the pool owner.
This invention provides a method for purifying aqueous liquids which substantially eliminates the need for using poisonous and irritating chemicals for sanitation purposes. The method includes use of a permeable, aqueous liquid purifying material containing a "biocatalyst" through which the liquid to be treated is circulated. The term "biocatalyst" is used herein to mean a microbicide or microbicidal catalyst composition in the form of a finely divided substance capable of being used in a filter medium through which the liquid to be treated is passed so that contact with the microbicide will destroy microorganisms, such as algae, protozoa, bacteria, and viruses present in the liquid. Thus, there is no need to add destructive, irritating, or poisonous chemicals to the liquid being treated. The method also avoids salt build-up caused by the addition of halogen-containing salts to the liquid. Further, there is no evaporative loss of costly sanitating agents such as chlorine or muriatic acid.
Although biocatalysts have been used in the past for various sterilization or sanitation purposes, it is believed that such biocatalysts have not been used reliably and economically in a system for purifying large bodies of water by recirculating the water through the filtering system. The present invention is based on the recognition that the effectiveness of a biocatalyst for purifying water circulated through a filtering system depends upon maintaining certain operating conditions to keep the biocatalyst active. For example, the present invention is based on a recognition that a biocatalyst filter cake can be rendered inactive by excess hydrogen atoms or high temperatures. A biocatalyst also can be "blinded", i.e., coated with a thin film of organic matter which renders the biocatalyst inactive. Furthermore, if the biocatalyst is physically disturbed or eroded, it can be circulated through the filtration system and thus rendered ineffective.
The present invention provides a method for preserving the biocatalyst filter cake from such destructive conditions so that the biocatalyst will be constantly maintained in an active condition during operation of the filtration system and thereby effectively purify the water.